Feature: Add SLIP-19 support for safe remote-signing of WabiSabi coinjoins#685
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kravens wants to merge 2 commits into
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Feature: Add SLIP-19 support for safe remote-signing of WabiSabi coinjoins#685kravens wants to merge 2 commits into
kravens wants to merge 2 commits into
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…or coinjoin remote signing
Taproot key-spend proof: BIP-86 tweak the internal key (libsecp keypair_xonly_tweak_add handles internal even-Y + output parity), then a BIP-340 schnorr signature over the same SLIP-19 digest. Simulator-verified against Wasabi OwnershipProof.VerifyOwnership with an independent NBitcoin BIP-86 derivation. Note: a full taproot coinjoin round also needs taproot PSBT spend-signing, which is EDGE-firmware only.
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SLIP-19 ownership proofs for coinjoin remote signing
What
Adds a USB command
slp9that returns a SLIP-19 ownership proof (BIP-322-style) for a given derivationpath + commitment, and an HSM policy field
slip19_pathsgating which paths may be proven while unattended.This is the one primitive a coinjoin coordinator (e.g. Wasabi WabiSabi) needs that no existing Coldcard
command provides: a signature over
SHA256(proofBody ‖ cs(spk) ‖ spk ‖ cs(commitment) ‖ commitment), whichis not a transaction sighash, so PSBT/BIP-322/message-signing cannot produce it.
Changes (3 files, ~84 lines)
shared/slip19.py(new) —make_ownership_proof(subpath, flags, commitment): derives the key,builds the proof body (
magic SL\x00\x19 ‖ flags ‖ varint(count) ‖ 32-byte ownership id), computes thedigest, ECDSA-signs (P2WPKH), and returns the fully serialized proof (proof body ‖ empty scriptSig ‖
witness stack). Taproot (P2TR, BIP-340 keyspend over the same digest) is stubbed — the
nguprimitives(
sign_schnorr,xonly_pubkey_tweak_add, tagged-sha256) are already present.shared/usb.py—slp9command handler mirroringsmsg/xpub: unpacks<III>(flags, len_subpath,len_commitment) + payloads, gates on
hsm_active.approve_slip19(subpath)when in HSM mode, returnsb'biny' + proof.shared/hsm.py—slip19_pathspolicy field (mirrorsmsg_paths), included in policy JSON/text, andapprove_slip19(subpath)(mirrorsapprove_xpub_share).Verified (simulator)
The real
slp9command returns a proof that Wasabi's own verifier accepts — see the consumer testsWalletWasabi.Tests/.../ColdcardProofSpikeTests.cs(OwnershipProof.VerifyOwnershippasses on both thereconstructed proof and the full wire bytes off the
slp9command).Before upstream submission (follow-ups)
sign_schnorr).not bind the id, but should be correct).
xpub; upstream may want an on-deviceconfirmation for interactive use (in HSM the
slip19_pathswhitelist is the gate).testing/test_hsm.pycoverage (whitelisted path signs, non-whitelisted denied) + a docs page.